In the current railway field, as a method for detecting a position of a train, a method in which an absolute distance received from a position correction track antenna installed on the ground is used as a starting point, and a relative distance to the position correction track antenna is measured from the number of rotations of wheels by a tachometer generator mounted on the train is mainstream. However, there is a problem in that a position of a train becomes inaccurate due to a failure in communication with a track antenna, an error of a wheel diameter caused by wear of a wheel or the like, and an idling slip of a wheel.
Accordingly, there is devised a method in which an absolute position of a train is constantly measured by GPS satellites. The positioning by the GPS (Global Positioning System) satellites is accompanied by a positioning error caused by a decrease in signal reception sensitivity, multipath or the like. Therefore, Patent Document 1 discloses a method in which a position of a train is determined in consideration of reliability of position accuracy based on the GPS satellites so as to control the train.